Paper documents which experience a lot of handling are subject to wear as a result of such handling. For example, documents such as paper currency are constantly being handled both manually and by mechanical processing means. Such constant handling subjects the paper currency to wearing and eventually the documents become so worn or limp, that they are no longer serviceable. Worn documents are preferably removed from public use and are destroyed in favor of new paper currency. The advantages of replacement of worn paper currency by new paper currency are both numerous and important, one such advantage being the ease and accuracy of handling new paper currency through mechanical means.
In this connection, it is important to be able to evaluate paper currency at high speed in order to establish its serviceability. Such examinations are typically conducted by institutions such as large banks which are responsible for handling tens of thousands and even hundreds of thousands of pieces of paper currency on a daily basis. Thus, it comes important to be able to process and examine paper currency at high speed and still be able to accurately classify the paper currency into serviceable or unserviceable categories. Only one such limpness detector is known to the present inventor, and comprises a limpness detector in which a pin is utilized to pierce the paper currency such that the force required to pierce through the currency is determinative of the limpness or stiffness of the paper currency. This technique has obvious disadvantages among which are the direct and significant contribution toward the destruction of the paper currency which is directly contrary to the normal objective of preservation of serviceable currency. Also, the technique of piercing the paper currency does not lend itself to high speed handling and to examination of the paper currency while it is moving at such high linear speeds.